The instant invention pertains to a control circuit for a pump, and more particularly to such a circuit which controls a pump of the type for pumping hydrocarbons which are floating on water.
One use for such pumps is for recovering spilled hydrocarbon products in and around facilities where such products are handled. For example, in a refinery, hydrocarbon products may spill onto the ground and seep downwardly until the water table is encountered. Over a period of years, thousands of gallons of hydrocarbons may float on the surface of the water table in and around the refinery.
In the past, wells have been drilled in order to recover such floating hydrocarbons. When such a well is dug, a first pump is lowered to the bottom of the well to pump water from the bore. As water is pumped from the bore, water surrounding the bore begins flowing toward the bore. The surface of the water table assumes an inverted cone shape centered about the bore. The hydrocarbons floating on the water table thus begin flowing on the surface of the inverted cone toward the well bore. Thus, the bore includes a lower column of water having an upper column of hydrocarbons floating on the water.
In order to recover the floating hydrocarbons in the bore, a second pump is lowered on a cable to the surface of the hydrocarbon/water interface. The pump includes a pump intake, a first electrical probe located at the pump intake, and a second electrical probe located about four inches beneath the pump intake. A common elongate probe is mounted against both the first and second probes. Adjacent the pump intake, a float is provided which switches a switch when the intake is immersed in liquid.
A power source is provided for energizing the pump and a control circuit is provided for selectively applying the power source to the pump. The prior art control circuit is formed substantially from transistors and diodes and receives inputs from the probes and from the float switch. The circuit applies voltage to the common probe and detects presence or absence of such voltage on each of the first and second probes. Presence of the common voltage on either of the probes indicates that the probes are immersed in water, such conducting the voltage to the probe. The absence of the voltage indicates that the probes are immersed in either the hydrocarbon, which has a very high resistance, or in air (also having a high resistance). Detection of the condition of the float switch indicates whether or not the pump is in liquid or in air. Thus, if the float switch indicates the pump is in liquid and the common voltage is not present at one of the probes, that probe is immersed in the hydrocarbon.
The prior art control circuit functions in one of two modes. In the first mode, the pump is lowered until the intake is just above the water/hydrocarbon interface. As the hydrocarbons flow into the bore, the weight of the hydrocarbons forces the interface downwardly until the lower probe is immersed in the hydrocarbon. At this point, the control circuit applies power to the pump, and a latch circuit latches the pump in an on condition until the pump pumps sufficient hydrocarbons so that both probes are again immersed in water. The circuit removes power from the pump until both probes are again received within the hydrocarbon.
In its second mode, when the high probe is in hydrocarbon, a time delay begins a timing period. At the end of the timing period, the pump is energized and the hydrocarbon is pumped until the high probe is again immersed in the hydrocarbon. This cycle is thereafter repeated.
This past control circuit is deficient in several respects. The circuit is formed from discrete components and is difficult to service and less reliable than integrated circuitry. Further, a problem is created in the old circuit due to the variation from well to well of the time in which a given amount of hydrocarbon flows into the bore. For example, when operating in the first mode in a fast well, the pump may be turning on and off very frequently.
In the second mode, a certain amount of trial and error setting of the time delay is necessary to prevent rapid on-and-off switching of the pump and to insure the pumps will be energized a sufficient amount of time.
It is a general object of the present invention to provide a pump control circuit for the above-described pump which overcomes the disadvantages of past circuits.
It is a more specific object of the invention to provide such a circuit which, although including a variable time delay, has only one mode of operation.
It is another specific object of the instant invention to provide such a circuit in substantially all integrated circuit form.
In the instant invention, the first and second probes as well as the float switch on the pump are operatively connected to an AND gate circuit. The AND gate circuit is operatively connected to a time delay which in turn is connected to a pump energization circuit. The AND gate circuit generates a signal which starts the time delay when both probes are immersed in a nonconducting liquid. After the timed period, the time delay provides a signal to the pump energization circuit which starts the pump. A latching circuit operatively connected to the probes, the float switch, and to the pump energization circuit maintains the pump in an energized condition until both probes are again immersed in a conducting liquid.
These and other objects and advantages attained by the instant invention will become more apparent as the following detailed description is read in view of the accompanying drawings.